Disc grinding apparatus



Aug. 11, 1970 o. A. LAAKSO DISC GRINDING APPARATUS 2 Sheets$heet 1 Filed Oct. 25, 1967 6% BY TM ATTORNEYS Aug. 11, 1970 o. A. LAAKSO 3,523,649

DISC GRINDING APPARATUS Filed Oct. 25, 1967 2 Sheets-Sheet 2 INVENTOR cwn'wzwbzab ATTORNEYS United States Patent DISC GRINDING APPARATUS Oliver A. Laakso, Glens Falls, N.Y., assignor to Aktiebolaget Kamyr, Karlstad, Sweden Filed Oct. 25, 1967, Ser. No. 678,000 Claims priority, application Sweden, Oct. 27, 1966, 14,747/ 66 Int. Cl. B02c 7/12 US. Cl. 241-85 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a grinding apparatus adapted for defibrating or refining of cellulosic material and particularly for such disintegration of fiber bundles as is required after chemical or semichemical digestion of wood chips or similar material in order to provide pulp suitable for the manufacture of paper or board.

The invention relates particularly to a grinding apparatus of the kind comprising two independently rotary grinding discs, the active faces of which are located in essentially the same plane perpendicular to the common axis of rotation. In a known design of such a grinding apparatus the two grinding discs which rotate in opposite directions are equal and work exclusively against each other. The relative linear velocity of the grinding discs varies in proportion to the radius and as too great differences thereof are unfavourable, the size of the grinding discs will be limited.

The present invention has for its object to evade said limitation and to make it possible to build a grinding apparatus of a great diameter and a great capacity without having such great differences of the relative velocities in the grinding gap as correspond to the quotient of the largest radius to the smallest radius of the active grinding faces.

The basic characterizing feature of the invention whereby said object is realized, consists in that the working faces of the two grinding discs are located in annular zones of different radial extensions. The grinding disc having the working zone of greater radii cooperates preferably with a stationary grinding disc. The other grinding disc which has the working zone of lesser radii can be put in rotation at such a speed as to cause an increased relative velocity of its grinding face relatively to its cooperating grinding face, whereby the differences of linear velocity in the grinding gap connected with the different radial distances of the various grinding areas, are partly equalized.

The invention will be more closely described herein below with reference to accompanying drawings in which FIGS. 1 and 2 are axial sectional views of two different embodiments.

In FIG. 1, 11 designates a larger grinding disc and 13 a smaller grinding disc. These discs are attached to free ends of separate shafts 15 and 17, respectively. Said shafts which are coaxial, are journalled in and sealed to a housing 19. A tangential inlet 21 for cellulosic material to be treated is located at the periphery of said housing. An outlet 23 for treated material is connected to the housing close to its central part. The discs 11 and 13 are pro- "Ice vided with grinding faces 25 and 27, respectively, which are situated in one and the same plane perpendicular to said shafts, and said discs are facing in the same axial direction. Opposite to said grinding faces the inner side of the housing is provided with a stationary grinding disc having grinding faces 29 and 31. All grinding discs have rough working faces, e.g. are shaped with teeth or similar protuberances in order to suitably grind or abrade the fibrous material passing through the gap therebetween. The larger grinding disc 11 has a central recess 33 which completely houses the smaller grinding disc 13 whereby its grinding face 27 can be placed accurately in the same .plane as the grinding face 25. Thus the grinding face 25 forms an annular Zone completely outside the annular zone formed by the grinding face 27, i.e. the working zones of the grinding discs have wholly different radial extensions. The outer pair of cooperating grinding faces 25, 29 may be adapted for a coarse treatment and may have rougher teeth, whereas the inner pair of cooperating grinding faces 27, 29 is adapted for finer treatment and has smaller teeth or similar. The material is supplied under overpressure so that the same is fed in the direction of the arrows against the action of the centrifugal force, first through the radially outer grinding gap and then through the radially inner grinding gap. The treated material is collected in a space close to the shaft 17 and departs therefrom through the outlet 23. In operation, the shafts 5 and 17 are turned preferably in the same direction but with different speeds. For instance, the shaft 15 may be turned with a speed of 700-1200 rpm. and the shaft 17 with a speed of 1700-3000 r.p.m. When said speeds are chosen, the grinding disc 11 may be made considerably larger than in grinding apparatus of similar known manufactures where the maximum diameter is limited by the high speed of rotation required for efficient grinding also at the central parts of the grinding disc. The mentioned comparatively low speed of rotation of the grinding disc 11 is of no disadvantage with respect to the grinding action performed by the disc 13 on account of the latter being driven independently and with a speed adapted to its desired operation. Thus, the coarse grinding and the fine grinding which follow each other during the radial inward movement of the fibrous material, will take place with linear speeds of grinding in the grinding gaps not necessarily proportional to the great differences of radii of the two treatment zones, but said speeds may be given the values most suitable for an efficient grinding operation.

In the embodiment shown in FIG. 2 the large rotary grinding disc 35 is provided with a grinding face extending over a considerable part of the available space in the radial direction and divided into an outer portion 37 and an inner portion 39. The outer portion 37 of the grinding disc cooperates with a grinding face 41 attached to the housing, whereas the inner portion 39 cooperates with a grinding face 43 formed upon the smaller rotary grinding disc 45. The latter is turned by its shaft in opposite direction to the grinding disc 35 and with a speed which may be equal to that of the grinding disc 35 but which can also be chosen higher or lower in order to have in the gap between the faces 39 and 43 a relative linear speed which is at least equal to and usually greater than the average relative linear speed in the gap between the faces 37 and 41. The grinding disc 45 has one or more through passages 47 which are placed radially inwards of the grinding face 43 and serve to let the ground material out to the opposite side of the disc 45 from where it can depart through the outlet 49 upon the housing 51. The inlet 53 is located at the periphery of the housing and the pulp is supplied therethrough under pressure so that it passes first between the grinding discs 35, 41 where it is subjected to a first step of grinding, coarse grinding,

and then between the grinding faces 39, 43 which may be adapted for effecting fine grinding. The two grinding face portions 35, 39 may join to form a continuous grinding face. In the latter case said disc may have a continuously Varying roughness, the face being increasingly finer in the direction towards the centre.

What is claimed is:

1. Apparatus for defibrating or refining of cellulosic material consisting of two independently rotary grinding discs, the active faces of which are located in substantially the same plane perpendicular to the common axis of rotation, characterized in that the working faces of the two grinding discs are located in annular zones of different radial extensions, the rotary grinding disc having the working zone of greater radii, cooperating with a stationary grinding disc.

2. Grinding apparatus according to claim 1, characterized in that the rotary grinding disc having the working zone of lesser radii, faces in the same direction as the other rotary grinding disc and cooperates with a second stationary grinding disc.

3. Grinding apparatus according to claim 1, characterized in that one rotary grinding disc is located in a central recess in the other rotary grinding disc, the entire working zone of the former being situated radially inwardly of the working zone of the latter.

4. Grinding apparatus according to claim 1, characterized in that the rotary grinding disc having the Working zone of lesser radii, faces and cooperates with a central portion of the other grinding disc, whereas the peripheral portion of the latter cooperates with a stationary grinding disc.

5. Grinding apparatus according to claim 4, characterized in that one rotary grinding disc has a through passage close to its shaft for passing ground material to an outlet upon the housing.

References Cited UNITED STATES PATENTS 9,313 10/1852 Barnett 241-162 X 525,582 9/1894 Bonnefond 241162 X 2,156,321 5/1939 Sutherland 241251 2,738,931 3/1956 Schneider 241162 FRANK T. YOST, Primary Examiner US. Cl. X.R. 

